Hydrocarbon mixtures, such as crude oils and certain fuel oils derived therefrom, may contain considerable amounts of wax. The wax present in crude oils and fractions thereof primarily consists of paraffins but may also contain some non-linear alkanes. This wax is normally dissolved in the oil but may precipitate from these hydrocarbon mixtures under certain circumstances. This precipitation may in particular happen when the hydrocarbon mixture is cooled. When the temperature is lowered sufficiently one may observe small wax crystals occurring in the fluid. These crystals may form deposits at surfaces and they will also significantly alter the flow properties, such as the viscosity, of the hydrocarbon fluid. In the production process of crude oil and gas, these phenomena pose significant challenges. The deposits may partially or fully block flowlines and when the viscosity has become too high, the liquids may not flow at all even when there are no or few deposits. The hydrocarbon mixture may even solidify completely.
Several methods exist to prevent or mitigate wax induced flow impairment. Examples include the insulation or heating of conduits, thus maintaining a high temperature of the fluids, regular “pigging” of flowlines, which comprises a method of mechanically scraping the inside of the flowlines in order to remove the deposits. However such methods are not always possible or economically viable.
This has led to the development of certain chemical compounds which when added to the said hydrocarbon fluids alter the effect of wax. Some compounds may reduce the cloud point, those are also known as wax inhibitors, and some reduce the pour point and these are also known as pour point depressants.
Various chemical compounds are known in the prior art to affect the wax deposition and flow behaviour of hydrocarbon fluids. These compounds are based on polymers with various chemical compositions. U.S. Pat. No. 3,447,916 describes linear polyesters or polyamides with side-branching based on a diacid or diacid anhydride, a monoacid and a polyol or hydroxylamine for use pour point depressants for fuel oils. European Patent Application EP-A 448166 describes polymer compositions comprising a polymer of an ethylenically unsaturated compound, such as C18-26 n-alkyl acrylates or copolymers of such acrylates and vinylpyridine
For a successful application of these products, various other properties are also relevant. For example, the viscosity of the solution in which these compounds are delivered. Sometimes these solutions have themselves a relatively high pour point. In circumstances where it is desired to pass the fluidity improvers along a pipeline in a cold environment, this is highly undesirable. This problem becomes relevant in the above-mentioned EP-A 448166 since the polymers used in the dispersions of this prior art have a molecular weight (Mn) of well above 10,000. Examples show molecular weights of 25,000 to 76,000. The prior art solves this problem by incorporating the polymer or copolymer in a dispersion that further contains a surfactant and a polyol. However, in cases were added fluids may come into contact with the environment, environmental properties, such as toxicity and biodegradability, also become relevant.